Tomcat is hanging on Stop

Vaadin 6 / 7 / 8
1

Environment: Tomcat 8.5.29, Vaadin 8.4.0,
When : @Push(transport=Transport.LONG_POLLING)
Log:

2-May-2018 12:40:12.193 WARNING [localhost-startStop-2]
 org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [managecat-controller]
 appears to have started a thread named [Atmosphere-Scheduler-0]
 but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.poll(ScheduledThreadPoolExecutor.java:1134)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.poll(ScheduledThreadPoolExecutor.java:809)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 java.lang.Thread.run(Thread.java:748)
22-May-2018 12:40:12.194 WARNING [localhost-startStop-2]
 org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [managecat-controller]
 appears to have started a thread named [Atmosphere-Shared-0]
 but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
 java.util.concurrent.LinkedBlockingQueue.poll(LinkedBlockingQueue.java:467)
 org.atmosphere.cpr.DefaultBroadcaster$1.run(DefaultBroadcaster.java:405)
 java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
 java.util.concurrent.FutureTask.run(FutureTask.java:266)
 java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
 java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
 java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
 java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
 java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
22-May-2018 12:40:12.194 WARNING [localhost-startStop-2]
 org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [managecat-controller]
 appears to have started a thread named [Atmosphere-Scheduler-1]
 but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.poll(ScheduledThreadPoolExecutor.java:1129)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.poll(ScheduledThreadPoolExecutor.java:809)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 java.lang.Thread.run(Thread.java:748)
2

I would recommend to upgrade to 8.4.2. There was a regression in 8.4.0 version of Atmosphere which caused problems with Tomcat. That may be one of the culprits here.